A new study uses a much-improved method to study fear in rats, but it raises …

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Animals’ lives are essentially all about food, sex, and fear. If you can escape predators long enough to eat and reproduce, your genes will live to see another generation. That’s why fear is so important: it’s a warning sign that something is wrong and, if you don’t address the threat, you might not make it to the next meal.

Normally, scientists study fear in nonhumans in a pretty artificial way. Captive animals are trained to associate a harmless stimulus—say, a red light or a tone—with a nasty shock. Soon, just hearing the tone or seeing a colored light will send them cowering into a corner. But, this has little semblance to the evolutionary basis of fear. A pair of researchers has developed a new methodology that mimics natural conditions so that they can study fear in a more realistic way, and the paper appears in this week’s PNAS.

One at a time, the researchers put a single rat into a large open space and allowed it to acclimatize and begin using a nest in the corner. They placed food pellets at various distances from the nest, from about 25 to 76 cm.

After at least five days of uninterrupted foraging time, the scientists introduced their secret weapon: Robogator. Robogator is a Lego Mindstorms robot that the researchers built to resemble a predator, with eyes, a moving mouth, and a lunging motion, all intended to scare the rats. Whenever the rat left its nest and headed toward a pellet, Robogator lunged and snapped its jaws. Check out the videos here.

Every time Robogator "attacked," the rats scurried back to their nests and froze. Eventually, they re-emerged and cautiously made another run at the pellet. Not surprisingly, after encountering Robogator, the rats were much more likely to grab the pellets closer to their nest (and farther from the threat). Every single rat adjusted its foraging behavior in this way when Robogator was around.

The researchers hypothesized that the amygdala was behind this fear behavior; by altering the activity of the rats' amygdalae, they were able to confirm their suspicions. Rats that had lesions made to their amygdalae had no fear whatsoever of Robogator, and rats that were given chemicals that left their amygdales uninhibited were so scared of Robogator that they barely made any attempts to get food. Obviously, being either completely unaffected or totally immobilized by a predator is not good for an animal’s evolutionary fitness.

So, how are rats deciding how far to venture for food when a threat is present? The answer isn't exactly clear yet. One working hypothesis presumes that the farther the food is from the nest or hiding place, the more easily the fear motivation overcomes the hunger motivation. It may be a battle of one motivation against another: to eat and satisfy hunger, or to stay safe from a predator's jaws.

Some scientists believe that some animals (even rats) are capable of performing complex calculations that estimate a predator's distance and velocity, as well as the animal's own speed and proximity to a safe place, to determine whether a risky move is likely to pay off. If they determine that the margin of safety is too small, they will play it safe. The fact that the rats with functioning amygdalae altered their behavior in a very specific way in response to Robogator lends some support to this idea, but further research is obviously needed.

From the results of this study, it's clear that the amygdala is instrumental in evaluating a looming threat against a need for resources. What isn't yet clear is how animals are able to weigh one motivation against another and decide on a course of action. While this study's findings aren't revolutionary or conclusive by any means, the quasi-naturalistic method the researchers employed seems like a much-improved way to study the proximate and ultimate bases of fear.

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Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida